Toward a realistic macroscopic parametrization of space plasmas with regularized κ-distributions

So-called κ-distributions are widely invoked in the analysis of nonequilibrium plasmas from space, although a general macroscopic parametrization as known for Maxwellian plasmas near thermal equilibrium is prevented by the diverging moments of order l ≥ 2κ − 1. To overcome this critical limitation, recently novel regularized κ-distributions (RK) have been introduced, including various anisotropic models with well-defined moments for any value of κ > 0. In this paper, we present an evaluation of the pressure and heat flux of electron populations, as provided by moments of isotropic and anisotropic RKs for conditions typically encountered in the solar wind. We obtained finite values even for low values of κ < 3/2, for which the pressure and heat flux moments of standard κ-distributions are not defined. These results were also contrasted with the macroscopic parameters obtained for Maxwellian populations, which show a significant underestimation especially if an important suprathermal population is present (e.g., for κ < 2), but ignored. Despite the collisionless nature of solar wind plasma, a realistic characterization as a fluid becomes thus possible, retaining all nonthermal features of plasma particles.

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HelioSwarm: The Nature of Turbulence in Space Plasmas

10.5194/egusphere-egu21-12092 ◽

2021 ◽

Author(s):

Harlan Spence ◽

Kristopher Klein ◽

HelioSwarm Science Team

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Large Scale ◽

Solar Wind Plasma ◽

Turbulent Energy ◽

Space Plasmas ◽

Plasma Parameters ◽

Astrophysical Plasmas ◽

Ion Distributions ◽

Background Magnetic Field

Recently selected for phase A study for NASA&#8217;s Heliophysics MidEx Announcement of Opportunity, the HelioSwarm Observatory proposes to transform our understanding of the physics of turbulence in space and astrophysical plasmas by deploying nine spacecraft to measure the local plasma and magnetic field conditions at many points, with separations between the spacecraft spanning MHD and ion scales.&#160;&#160;HelioSwarm resolves the transfer and dissipation of turbulent energy in weakly-collisional magnetized plasmas with a novel configuration of spacecraft in the solar wind. These simultaneous multi-point, multi-scale measurements of space plasmas allow us to reach closure on two science goals comprised of six science objectives: (1) reveal how turbulent energy is transferred in the most probable, undisturbed solar wind plasma and distributed as a function of scale and time; (2) reveal how this turbulent cascade of energy varies with the background magnetic field and plasma parameters in more extreme solar wind environments; (3) quantify the transfer of turbulent energy between fields, flows, and ion heat; (4) identify thermodynamic impacts of intermittent structures on ion distributions; (5) determine how solar wind turbulence affects and is affected by large-scale solar wind structures; and (6) determine how strongly driven turbulence differs from that in the undisturbed solar wind.&#160;

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Role of Whistler Waves in Regulation of the Heat Flux in the Solar Wind

10.5194/egusphere-egu2020-1175 ◽

2020 ◽

Author(s):

Ilya Kuzichev ◽

Ivan Vasko ◽

Angel Rualdo Soto-Chavez ◽

Anton Artemyev

Keyword(s):

Magnetic Field ◽

Heat Flux ◽

Solar Wind ◽

Particle Interaction ◽

Solar Wind Plasma ◽

Whistler Waves ◽

Particle In Cell ◽

Electron Heat ◽

Background Magnetic Field ◽

Institute Of Technology

The electron heat flux is one of the leading terms in energy flow processes in the collisionless or weakly-collisional solar wind plasma. The very first observations demonstrated that the collisional Spitzer-H&#211;&#147;rm law could not describe the heat flux in the solar wind well. In particular, in-situ observations at 1AU showed that the heat flux was suppressed below the collisional value. Different mechanisms of the heat flux regulation in the solar wind were proposed. One of these possible mechanisms is the wave-particle interaction with whistler-mode waves produced by the so-called whistler heat flux instability (WHFI). This instability operates in plasmas with at least two counter-streaming electron populations. Recent observations indicated that the WHFI operates in the solar wind producing predominantly quasi-parallel whistler waves with the amplitudes up to several percent of the background magnetic field. But whether such whistler waves can regulate the heat flux still remained an open question.We present the results of simulation of the whistler generation and nonlinear evolution using the 1D full Particle-in-Cell code TRISTAN-MP. This code models self-consistent dynamics of ions and two counter-streaming electron populations:&#160; warm (core) electrons and hot (halo) electrons. We performed two sets of simulations. In the first set, we studied the wave generation for the classical WHFI, so both core and halo electron distributions were taken to be isotropic. We found a positive correlation between the plasma beta and the saturated wave amplitude. For the heat flux, the correlation changes from positive to a negative one at some value of the heat flux. The observed wave amplitudes and correlations are consistent with the observations. Our calculations show that the electron heat flux does not change substantially in the course of the WHFI development; hence such waves are unlikely to contribute significantly to the heat flux regulation in the solar wind.The classical WHFI drives only those whistler waves that propagate along the halo electron drift direction (consequently, parallel with respect to background magnetic field). Such waves interact resonantly with electrons that move in the opposite direction; hence, only a relatively small fraction of hot halo electrons is affected by these waves. On the contrary, anti-parallel whistler waves would interact with a substantial fraction of halo electrons. Thus, they could influence the heat flux more significantly. To test this hypothesis, we performed the second set of simulations with anisotropic halo electrons. Anisotropic distribution drives both parallel and anti-parallel waves. Our calculations demonstrate that anti-parallel whistler waves can decrease the heat flux. This indicates that the waves generated via combined whistler anisotropy and heat flux instabilities might contribute to regulation of the heat flux in the solar wind.The work was supported by NSF grant 1502923. I. Kuzichev would also like to acknowledge the support of the RBSPICE Instrument project by JHU/APL sub-contract 937836 to the New Jersey Institute of Technology under NASA Prime contract NAS5-01072. Computational facility: Cheyenne supercomputer (doi:10.5065/D6RX99HX) provided by NCAR&#8217;s Computational and Information Systems Laboratory, sponsored by NSF

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A FEASIBILITY STUDY OF EMPLOYING SEQUENTIAL FUNCTION SPECIFICATION METHOD FOR ESTIMATION OF TRANSIENT HEAT FLUX IN A NON-THERMAL EQUILIBRIUM POROUS CHANNEL

Journal of Porous Media ◽

10.1615/jpormedia.v14.i5.10 ◽

2011 ◽

Vol 14 (5) ◽

pp. 375-381

Author(s):

Mohsen Nazari ◽

Farshad Kowsari

Keyword(s):

Heat Flux ◽

Feasibility Study ◽

Thermal Equilibrium ◽

Porous Channel ◽

Specification Method ◽

Sequential Function Specification ◽

Function Specification Method ◽

Transient Heat Flux

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A review of the SCOSTEP’s 5-year scientific program VarSITI—Variability of the Sun and Its Terrestrial Impact

Progress in Earth and Planetary Science ◽

10.1186/s40645-021-00410-1 ◽

2021 ◽

Vol 8 (1) ◽

Author(s):

Kazuo Shiokawa ◽

Katya Georgieva

Keyword(s):

Solar Wind ◽

Interplanetary Space ◽

Solar Wind Plasma ◽

The Sun ◽

Scientific Program ◽

Solar Cycles ◽

Grand Minimum ◽

The Earth ◽

Earth Connection ◽

Near Future

AbstractThe Sun is a variable active-dynamo star, emitting radiation in all wavelengths and solar-wind plasma to the interplanetary space. The Earth is immersed in this radiation and solar wind, showing various responses in geospace and atmosphere. This Sun–Earth connection variates in time scales from milli-seconds to millennia and beyond. The solar activity, which has a ~11-year periodicity, is gradually declining in recent three solar cycles, suggesting a possibility of a grand minimum in near future. VarSITI—variability of the Sun and its terrestrial impact—was the 5-year program of the scientific committee on solar-terrestrial physics (SCOSTEP) in 2014–2018, focusing on this variability of the Sun and its consequences on the Earth. This paper reviews some background of SCOSTEP and its past programs, achievements of the 5-year VarSITI program, and remaining outstanding questions after VarSITI.

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